This invention relates to a solenoid drive system for an automatic performing apparatus having actuating keys such as a piano or key board. The solenoid drive system stores voltage waveform data in sequence according to performance information. The voltage waveform data comprises the intensity of key depression and is provided for each respective key number. Solenoids, also provided for each of the keys, are activated upon output of the voltage waveform data, thereby automatically recreating the performance.
A variety of methods have been proposed to control the value of power voltage supplied to solenoids in an automatic performing apparatus such as an automatic piano. One such method is duty cycle control, whereby the duty cycle of a square wave is changed. The duty cycle control is most favorable since it minimizes the electricity loss in a transistor utilized as switching element.
U.S. Pat. No. 4,132,141 discloses an apparatus adopting the duty cycle control method. The apparatus first generates pulses of a constant width, and then modulates the pulse width in accordance with key depression intensity.
When it comes to driving a plurality of keys individually but simultaneously, however, the above apparatus requires a corresponding plurality of digital to analog converters (DAC's) and modulation circuits, thus complicating the circuit structure. Moreover, because of the need for a DAC and modulation circuit, high precision apparatus control is hampered and requires intricate adjustment. Further, a voltage comparator included in the modulation circuit tends to deteriorate after a long period of use, revealing its drawback in durability.